Effect of polyols and diisocyanates on thermo-mechanical and morphologicalproperties of polyurethanes

Polyurethanes based on two polyols PPG (polypropylene glycol) and HTPB (hyd roxy terminated polybutadiene) and diisocyanates TDI (toluene diisocyanate) and MDI (methylene diphenyl diisocyanate) were synthesised using three dif ferent concentrations of the crosslinker 1,1,1-trimethylolpropane (TMP) at NCO : OH equivalent ratio 1.2 and 1.3. The mechanical, thermal and morpholo gical properties were investigated. HTPB/TDI system showed highest tensile strength whereas PPG/MDI system exhibited highest elongation at break, In d ifferential scanning calorimetry (DSC) thermograms transition for soft segm ent was observed to be considerably higher in PPG based polyurethanes (PUs) . The dielectric constant was also found to be higher in PPG based PUs. The tan delta(max) was found to lie in the range 0.7-1.0. From swelling behavi our the solubility parameter for PPG and HTPB based PUs was found to be 9.7 and 8.6 (cal/cm(3))(1/2), respectively. The molecular weight between cross links were determined by using the Flory-Rehner equation. (C) 2000 Elsevier Science Ltd. All rights reserved.